1. Field of the Invention
The present invention relates in general to a diathermy apparatus which therapeutically heats internal body tissue by irradiating the tissue with RF energy. In particular, the present invention discloses a method and apparatus for accurately measuring and controlling the amount of RF power being absorbed by the body tissue with the irradiating region of the diathermy apparatus. Specifically, the present invention relates to a diathermy apparatus which automatically tunes an applicator head of the apparatus.
2. Description of the Related Art
Medical diathermy involves the use of high frequency electric current for the therapeutic treatment of body tissue. This technique involves the transcutaneous transmission of high frequency energy to internal body tissues. The irradiated RF energy generates heat within the internal body tissue, having a therapeutic effect. This deep heating action produced by the diathermy apparatus is used to treat a number of varied ailments.
A diathermy apparatus typically generates high frequency electric currents which are provided to an applicator head for controllable application to the body tissue to be treated. The high frequency currents produced in a diathermy apparatus typically have a standard frequency of 27.12 MHz, which is within the permissible frequency range allocated for diathermy service. At this frequency, nerves and muscles are not adversely stimulated by the radiated energy, and the temperature produced in the internal body tissue is well below that required to destroy the tissue or impair its vitality.
Prior art diathermy machines typically are constructed of a single cabinet which houses the electrical circuitry and the display portion of the shortwave electrical therapeutic apparatus. Typically, a pair of movable arms extend outwardly from the cabinet, each of which positions a diathermy head at its outer end.
The applicator head of the diathermy apparatus includes a radiating electrode which is comprised of an induction coil that generates electromagnetic and electrostatic energy in response to the high frequency electric currents flowing through the electrode. The generated electromagnetic and electrostatic energy is then controllably applied by the applicator head to the body of the patient. This energy causes heat to be generated in the internal body tissue, which is within the radiating region of the head. U.S. Pat. No. 3,800,802 entitled "Short-Wave Therapy Apparatus" to Berry, et al., issued Apr. 2, 1974, and U.S. Pat. No. 4,210,152 to Berry entitled "Method and Apparatus for Measuring and Controlling the Output Power of a Shortwave Therapy Apparatus", issued Jul. 1, 1980, disclose diathermy machines which are utilized to apply RF energy to the human body for therapeutic purposes. These patents are incorporated herein by reference.
Of the energy generated by a diathermy apparatus, only the electromagnetic energy is useful in therapy. The electrostatic energy field that is generated simply heats the surface area of the human skin without deep penetration, and is therefore undesirable. Electrostatic shields, of the type shown, in U.S. Pat. No. 4,068,292 to Berry, et al. entitled "Electrostatic Shield for Diathermy Treatment Head", issued Jan. 10, 1978, and U.S. Pat. No. 4,281,362 to Berry entitled "Electrostatic Shield for Diathermy Treatment Head", issued Jul. 28, 1981, are conventionally used to attenuate the electrostatic energy field. These patents are incorporated herein by reference. U.S. Pat. No. 4,510,937 to Rogers entitled "Method and Apparatus for Operating Dual Diathermy Applicator Heads in Close Proximity to One Another", issued Apr. 16, 1985, discloses a method and apparatus for simultaneously operating two diathermy treatment heads in close proximity without interference caused by phase and frequency differences. This patent is incorporated herein by reference.
Elimination of the electrostatic field, through the use of an electrostatic shield, significantly improves the operating efficiency of the diathermy apparatus and the accuracy of the power measurement. Particularly, the interposition of an electrostatic shield between the generating electrode and the applicator head and the treated body tissue significantly reduces the electrostatic (capacitive) coupling between the body tissue and the applicator head, thereby making the reactive parameters of the head less responsive to the surface characteristics of the human load within the irradiating region of the applicator head. By eliminating capacitive coupling between the applicator head and the body tissue, the operating parameters of the diathermy apparatus no longer vary erratically in response to the surface characteristics of the load within the irradiating region of the head. Since the operating parameters of the device do not vary in response to the surface characteristics of the load, the level of power being provided to the applicator head only varies in response to the level of power actually being absorbed by the treated body tissue. While the introduction of body tissue into the irradiating region of the applicator head still causes some minor disturbances in the electrical operation of the power generating equipment, these disturbances are much smaller in magnitude and can be accurately measured. Furthermore, these minor disturbances are predictable and can be accounted for during the power computation.
Elimination of the electrostatic field also stabilizes the operation of the diathermy apparatus because the applicator head is less likely to be detuned from resonance on the introduction of a load into the irradiating region of the head. Therefore, it is easier to keep the current voltage locked in phase, thereby greatly enhancing the operation of the diathermy apparatus and improving the accuracy of the power measurement.
In order to properly and efficiently utilize the electromagnetic field that is generated by the applicator head of the diathermy apparatus, the circuitry associated with the apparatus should be tuned and the power applied to the patient should be closely controlled at a desired level. As the patient moves, or the body temperature or circulation of the patient changes, the load can vary rather widely. To compensate for such expected changes in the load, tuning devices are desirable because they continuously maintain the head tuned to a resonate condition to assure maximum power transfer from the applicator head to the patient load.
In the past, a variety of mechanical tuning components have been utilized for tuning the applicator head to a resonate condition. For example, variable capacitors have been utilized so that an operator of the diathermy apparatus could manually adjust the capacitor to maintain the device in a tuned state. Many such devices utilized a servo mechanism to achieve the tuning. Typically, the prior art utilizes a variable capacitor and a mechanical motor for physically driving the capacitor. The motor is coupled to a servo mechanism which controls a tuning element in the applicator head. The tuning element (e.g., variable capacitor) is varied in order to keep the applicator head in electrical resonance, thereby maintaining phase lock between the sensed current and voltage, and thus maintaining the amount of power being absorbed by the treated body tissue at a desired level.
The mechanical tuning mechanisms utilized in the prior art which require the operator to continuously vary the power are undesirable because of the very requirement that the operator must continually monitor and adjust the device. Those prior art devices requiring variable capacitors, servo mechanism and motors are overly cumbersome, require multiple components, and increase the overall expense of the device, and are therefore undesirable.
The need exists for a diathermy apparatus for generating and providing RF power in a simple manner. The need also exists for a diathermy apparatus which is more portable than prior art machines, and which automatically tunes the diathermy apparatus in a simple and efficient manner. The need also exists for a diathermy apparatus which easily and accurately displays on visual presentation of the actual power being used by a satellite load. These and other needs are met by the unique diathermy apparatus of the present invention while the foregoing and other drawbacks of the prior art are overcome.